The past few weeks have been bedlam for Dr Christopher Parry. His Tuesday afternoon clinic held in the centre of Colchester, Essex, offering single measles, mumps and rubella vaccines to the children of parents worried by MMR has been overwhelmed.

"They have come from Wales, from the North, from all over. It's madness," said a receptionist at his vaccination clinic yesterday.

His appointment book is full until the end of July but callers were being told yesterday that a second clinic could start next month to cope with the demand. The charge is £75 a vaccine, making £225 for the course of three.

Parents are willing to pay the high charges because few doctors are prepared to provide the single vaccines and they are in short supply. The single vaccines are unlicensed in this country and must be ordered individually on a "named patient" basis.

Dr Parry is likely to receive more than £40,000 in gross fees from his Tuesday afternoon clinics in the next six months. His clinic runs from 1.30pm to 6pm and he vaccinates five children an hour, yielding a gross income of about £1,600 for the afternoon.

Dr Parry, an NHS GP, backs the MMR vaccination but insists doctors must respond to demand. "I think MMR is safe and I have given it to my three boys. But people are not convinced of its safety and therefore will opt to have nothing. I think single vaccines are slightly less safe [than MMR] but they are better than nothing."

He defended the high charges saying he had had to hire a receptionist and a "bevy of maidens" to cope with the volume of calls from worried parents in the past few weeks. "I started last May doing it for a couple of afternoons a week seeing 10-15 patients an afternoon. Now it has taken off and I am really stretched.

"If I am accused of cashing in I would say I cashed in on it well before the latest hullabaloo – and the driving force has been the refusal of parents to have MMR. I could be accused of cashing in but I am offering a pretty sensible service."

Dr Parry said he obtained his vaccine supplies from IDIS World Medicines in Surbiton, Surrey. There had been a hiccup in the supply but he was expecting fresh vaccine to be available next week. IDIS was not returning calls yesterday.

For his own NHS patients, Dr Parry said he would administer the single vaccines without charge, but they would have to obtain the vaccines themselves. "I would advise them to have MMR but if they say no, and put it in writing then I would give them a private prescription to take to the chemist. I would never dream of denying my NHS patients a service I was happy to provide privately."

A spokeswoman for Boots said that a patient with a private prescription for measles or mumps vaccine would have to have it ordered individually, and the cost would be £50 to £60 for each vaccine. Rubella vaccine is licensed, because it is given to pregnant women, and would be "much cheaper", the spokeswoman said.

In Louth, Lincolnshire, Dr Peter Mansfield's "Good Healthkeeping" clinic had been inundated with 10,000 calls a day, a receptionist said yesterday. There are eight staff taking calls and the single vaccine clinic, which runs on Mondays, Tuesday and Thursdays, is fully booked until April.

Dr Mansfield, an energetic proselytiser for single vaccines, was reported to the General Medical Council last year by the local director of public health for setting up a clinic in Worcestershire but the charges were later dropped.